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Full-Text Articles in Physics

Inelastic Collisions And Anisotropic Aggregation Of Particles In A Nematic Collider Driven By Backflow, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich Jan 2011

Inelastic Collisions And Anisotropic Aggregation Of Particles In A Nematic Collider Driven By Backflow, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We design a nematic collider for controlled out-of-equilibrium anisotropic aggregation of spherical colloidal particles. The nematic surrounding imparts dipolar interactions among the spheres. A bidirectional backflow of the nematic liquid crystal in a periodic electric field forces the spheres to collide with each other. The inelastic collisions are of two types, head to tail and head to head. Head-to-tail collisions of dipoles result in longitudinal aggregation while head-to-head collisions promote aggregation in the transversal direction. The frequency of head-to-head collisions is set by the impact parameter that controls the resulting shape of aggregates, their anisotropy, and fractal dimension.


Polar And Nonpolar Orderings In The Electrically Induced Isotropic-Nematic Phase Transition, Mingxia Gu, Sergij V. Shiyanovskii, Oleg Lavrentovich Oct 2008

Polar And Nonpolar Orderings In The Electrically Induced Isotropic-Nematic Phase Transition, Mingxia Gu, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We study the dynamics of the isotropic-nematic phase transition caused by an applied electric field at the time scales of dielectric relaxation. In the classic Landau-Khalatnikov theory of the phase transition dynamics, the nematic (nonpolar) order parameter is an instantaneous function of the applied field. We demonstrate that, when the field is changing faster than the time of dielectric relaxation, the induced polar order dynamics influences the dynamics of the nonpolar order parameter. We develop a model based on the Langevin equation to describe the simultaneous dynamics of both polar and nonpolar order parameters; the model is supported by experiment.


Observation Of A Possible Tetrahedratic Phase In A Bent-Core Liquid Crystal, D. B. Wiant, K. Neupane, S. Sharma, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli, N. Pradhan, G. Iannacchione Jun 2008

Observation Of A Possible Tetrahedratic Phase In A Bent-Core Liquid Crystal, D. B. Wiant, K. Neupane, S. Sharma, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli, N. Pradhan, G. Iannacchione

Chemical Physics Publications

An experimental study of the heat capacity, mass density, magnetic-field-induced optical birefringence, linewidth and intensity of scattered light, and the viscosities associated with nematic order parameter fluctuations and fluid flow has been performed on an achiral bent-core liquid crystal above its clearing point temperature. The measurements reveal a transition between two optically isotropic phases that is consistent with recent theoretical predictions of a "tetrahedratic" form of orientational order.


Optically Isotropic Liquid-Crystal Phase Of Bent-Core Molecules With Polar Nanostructure, Guangxun Liao, S. Stojadinovic, Gerhard Pelzl, Wolfgang Weissflog, Samuel N. Sprunt, Antal Jakli Aug 2005

Optically Isotropic Liquid-Crystal Phase Of Bent-Core Molecules With Polar Nanostructure, Guangxun Liao, S. Stojadinovic, Gerhard Pelzl, Wolfgang Weissflog, Samuel N. Sprunt, Antal Jakli

Chemical Physics Publications

We found that the optically isotropic (I-M) mesophase observed recently below the nematic phase of the bent-core liquid crystal 4-chlororesorcinol bis[4-(4-n-dodecyloxybenzoyloxy)benzoate] shows ferroelectric-type switching. Polarizing microscopic, electric current, dielectric, and dynamic light scattering studies lead us to propose that the I-M phase is composed of interconnected orthoconic racemic smectic (Sm-CaPF) nanodomains with random layer orientations. Near the nematic phase, where the polarization can be saturated by electric fields, the system responds in a fashion analogous to the granular structure of a magnetic spin glass-in particular, we observed that the relaxation back to the nonpoled structure follows a ...


Ordered Droplet Structures At The Liquid Crystal Surface And Elastic-Capillary Colloidal Interactions, Ivan I. Smalyukh, S. Chernyshuk, B. I. Lev, A. B. Nych, U. Ognysta, V. G. Nazarenko, Oleg Lavrentovich Sep 2004

Ordered Droplet Structures At The Liquid Crystal Surface And Elastic-Capillary Colloidal Interactions, Ivan I. Smalyukh, S. Chernyshuk, B. I. Lev, A. B. Nych, U. Ognysta, V. G. Nazarenko, Oleg Lavrentovich

Chemical Physics Publications

We demonstrate a variety of ordered patterns, including hexagonal structures and chains, formed by colloidal particles (droplets) at the free surface of a nematic liquid crystal (LC). The surface placement introduces a new type of particle interaction as compared to particles entirely in the LC bulk. Namely, director deformations caused by the particles lead to distortions of the interface and thus to capillary attraction. The elastic-capillary coupling is strong enough to remain relevant even at the micron-scale when its buoyancy-capillary counterpart becomes irrelevant.


Dynamics Of The Nematic Phase Of A Bent-Core Liquid Crystal, S. Stojadinovic, A. Adorjan, Samuel N. Sprunt, Hans Sawade, Antal Jakli Dec 2002

Dynamics Of The Nematic Phase Of A Bent-Core Liquid Crystal, S. Stojadinovic, A. Adorjan, Samuel N. Sprunt, Hans Sawade, Antal Jakli

Chemical Physics Publications

The dielectric fluctuations in the uniaxial nematic phase of a bent-core liquid crystal have been studied by dynamic light scattering. Polarization selection of the scattering cross-section reveals one mode due to ordinary director fluctuations and, in the lower part of the nematic phase, a second mode attributable to fluctuations of the biaxial order parameter. The director fluctuations are similar to100 times slower than observed in typical nematics based on straight-core molecules, suggesting that the bent core nematogenic units may be microscopic smectic domains ("cybotactic" clusters).